FL70 walkthrough conversion possible?

[cqrmskt]

I have a Freighliner FL-70 and want to cut a hole in the cab and the box to make a pass through walkway. I took the truck to 2 mechanics to get a quote for doing this, one of them told me that I can't cut the back of the cab really wide like this photo unless I put in supports:


(From this thread)

He said if I didn't want to put in supports, it would have to be something like this:


(From this thread)

I don't think he does this sort of work normally though. Attached are some photos of my truck--can you guys give me your opinion of whether I can open the back wide, or if I need to make it small? (I would be replacing the bench seat with a bucket seat.)

As an alternative, I was considering cutting a walkthrough not in the middle of the cab but behind the passenger side, partially because then I would only have to cut out one whole window and not both or a bit of each. I would replace the bench seat with a bucket seat but placed in the middle because cuddling the driver is easier with a middle seat Is this doable?

I have been looking to find information on how to do this, but it's been difficult to find DIY instructions for this application, I can only find them for pickup trucks. So here is a wall of questions that I have.

• What kind of saw(s) do I use? The box has FRP walls with some kind of metal on the bottom part of the wall on the interior (see IMG_6266).
• Do I have to prep the edges with anything after sawing?
• Since the wall of the box is 5/8" thick (and idk how thick the cabin wall would be), I'm going to have to attach a flat bar or something to make a flange for the boot--does this bar go on the exterior or interior? If it goes on the interior, what sealant do I use to make sure water doesn't get into the plywood of the FRP walls and the cab walls?
• According to accordionboot.com I don't need a sealant. In your experience, is it air/weather tight without a sealant?
• IMG_6268 is a photo of the back of the cab from the passenger side, under the box. Is there anything special I need to consider with this?

Any info would be great. This is my first time doing anything like this and I want to make sure I do a good job. Thank you!! ^_^

[superbird03]

I plan to do the same with my t2000 to FRP box, however all the cuts I have made through my frp which includes window openings, doors, slideouts, vents etc.... I have done 2 coats of urethane on all the freshly cut wood. If water gets in there it will delaminate and will be ruined. I have cut my pass through yet and am not sure how that looks but I would think some kind of silicone around the edge wouldn't hurt.

As far as cutting the FRP, I just use a carbide tipped blade on my circular saw and either a jig saw or saw sawzall for the corners. The FRP is pretty hard on blades. As far as the back of your truck wall, I would use the same circular saw blade as it is thin sheet metal and will cut it pretty well. The blade will be junk when you are done but it will be straighter than trying to cut it out with a sawzall.

Steve

[cqrmskt]

Thanks for the info Steve

I have an angle grinder and a diamond blade--would that be sufficient?

For the urethane, do you mean something like this?
Tremco 10.1-oz. Buff Vulkem 116 Polyurethane Sealant-7103012 - The Home Depot

And to cut the metal on the bottom of the interior box wall (if I need to), would the diamond or carbide blade work? Does this type of blade work?
Dremel 3 in. Steel Metal Cutoff Wheels (3-Pack)-SM510C - The Home Depot

[superbird03]

The diamond blade or steel metal cutoff wheel will cut the steel no problem, but it isn't going to cut the FRP. You will need some kind of wood blade to cut the FRP. I think that sealant would work. I like using 100% silicone.

[bushpilot]

I'm no structural engineer (hell i didn't even sleep at a holiday inn last night)...but that horizontal "reinforcement" in this picture (below) seems inadequate....some VERTICAL stocks even if it didn't cross the window would increase the rigidity.

[Bob86ZZ4]

My truck is an '02 FL112. It's pretty similar to the FL70 I think. Here's the cutout on mine:

[Bob86ZZ4]

I'm sorry I don't have any pictures from the cab side. The floor of the cab is slightly higher than the floor of my living quarters. I'm guessing the builder wanted to leave metal around the opening for structural reasons? Rather than cutting out the entire back panel of the cab you know. My truck was ordered from Freightliner brand new to be built into the camper. I don't know if the cutout was done by Freightliner or United Specialties. U/S is out of business so can't call them and ask. I think it would be pretty awkward to climb through a narrow opening. I wish my opening was larger. I have to duck down and step over to get through it. It also makes it more difficult to converse with guests while driving down the road. I'd say cut it as big as you can but leave several inches of the back wall all the way around the cab. I don't know if they put any type of reinforcement around my cutout. It's all carpeted on the cab side so I can't see anything. I'd cut it out and then try pushing the cab side to side. If there is any flex weld in some reinforcements.

[Bob86ZZ4]

Maybe one of the bigger builders would give you some advice. Like Showhauler or Renegade, or Hawk, or Haulmark?

[hot rod]

I'm not sure how close your cap wall is to my GMC 6500, but when I did mine I left the upper curve of the the rear window frame, and cut straight down on both sides, then across right at floor level. Then a sheet of steel with a matching cutout became the front wall of the new box, which got bolted all the way around the sides and top, and welded with a piece of angle iron covering the bottom joint. Ended up very rigid, no weird flexes or creaks driving, and no boot to leak, just a nice bead of auto body seam sealer around the outside.

I know your situation is different as you have to use a boot, but I guess the point is don't be afraid to cut a big hole, every factory conversion has one, no big deal. Me being in the habit of maybe overthinking things, I'd probably agree with your mechanics that you'd want to reinforce the edge of the cut sheet metal to keep it stiff. Maybe a framework of small square tubing? Set back from the edge enough to allow the boot to slip onto the sheet metal edge. Of course I don't know what is available for boots, there might be something that is big enough to slip over say 1/2" square tubing, just bend the tubing in the shape of your opening and weld it in place. Just brainstorming as I type.