Truck Conversion & Toterhome Community - View Single Post

asitool · 11-04-2016, 11:14 AM

1) Thoughts on adding a pickup bed (or making some sort of bed type setup)
2) Any sort of run-down or basics page for construction of your own box, be it for just storage or a living area

(1) Yes, here are some thoughts.... I wanted to do some testing before really putting it out there, however We're putting a 5x8' "bed" sideways on the rear of a short box (13 foot box) class 8 motorhome. The "bed" will fold up flat against the rear of the coach (with lights in the back and bottom), then fold down flat when used for a patio deck or extra storage, or (we're still working this out but we think we can mount a gooseneck hitch in it). Normally, you tow with the 5th wheel / gooseneck over the wheels but with the weights involved the engineer says we'll be fine. It will tow a bit more like a bumper pull because of the swing involved in the overhang.

(2) Building the box. Often you'll see condensation on the outer skin at the location of the frame members of the box. This can be avoided by reducing the thermal bridging...heat transfer through the box walls. We've had good results with a 2x2 steel frame, (.090 if it needs to be structural, or .065 if less so), with 2" foam insulation in between the box frame members. We use 1/2" foam on the exterior, then 1/2 plywood over that, covered by aluminum. On the interior we use 1/2" foam, covered by 3/8 plywood covered by interior paneling. This results in a wall that is 4" thick, so you have to order your windows accordingly. It is much better insulated than most, heavier, and a has solid feel. The foam on both sides of the box frame reduces thermal bridging and although I don't have any engineering data, it seems to make a lot more difference than the R value of the foam itself. You also loose overall interior space in the width of the coach with the 4" walls.

You could cut down on those thicknesses by using 1 1/2 square tube, which would result in a 25% weight savings. I've found that using thinner plywood on the exterior results in a wavy side when installed over foam.

If you're not as concerned with insulation you can eliminate the foam on either side of the frame and go with thinner 1/4 or 1/8" luan on either side.

As others have said... It will cost more than you think. IMO, the only reasons to build it yourself are if you think it will be fun, or you can't buy what you really want. It will also help if you have a space and tools to do the build. It will be very expensive to pay someone else to build it for you.

11-04-2016, 11:14 AM	#8
asitool Member Join Date: Jul 2012 Posts: 57	1) Thoughts on adding a pickup bed (or making some sort of bed type setup) 2) Any sort of run-down or basics page for construction of your own box, be it for just storage or a living area (1) Yes, here are some thoughts.... I wanted to do some testing before really putting it out there, however We're putting a 5x8' "bed" sideways on the rear of a short box (13 foot box) class 8 motorhome. The "bed" will fold up flat against the rear of the coach (with lights in the back and bottom), then fold down flat when used for a patio deck or extra storage, or (we're still working this out but we think we can mount a gooseneck hitch in it). Normally, you tow with the 5th wheel / gooseneck over the wheels but with the weights involved the engineer says we'll be fine. It will tow a bit more like a bumper pull because of the swing involved in the overhang. (2) Building the box. Often you'll see condensation on the outer skin at the location of the frame members of the box. This can be avoided by reducing the thermal bridging...heat transfer through the box walls. We've had good results with a 2x2 steel frame, (.090 if it needs to be structural, or .065 if less so), with 2" foam insulation in between the box frame members. We use 1/2" foam on the exterior, then 1/2 plywood over that, covered by aluminum. On the interior we use 1/2" foam, covered by 3/8 plywood covered by interior paneling. This results in a wall that is 4" thick, so you have to order your windows accordingly. It is much better insulated than most, heavier, and a has solid feel. The foam on both sides of the box frame reduces thermal bridging and although I don't have any engineering data, it seems to make a lot more difference than the R value of the foam itself. You also loose overall interior space in the width of the coach with the 4" walls. You could cut down on those thicknesses by using 1 1/2 square tube, which would result in a 25% weight savings. I've found that using thinner plywood on the exterior results in a wavy side when installed over foam. If you're not as concerned with insulation you can eliminate the foam on either side of the frame and go with thinner 1/4 or 1/8" luan on either side. As others have said... It will cost more than you think. IMO, the only reasons to build it yourself are if you think it will be fun, or you can't buy what you really want. It will also help if you have a space and tools to do the build. It will be very expensive to pay someone else to build it for you.