Fire trucks and engines are well cared for as far as keeping them clean and maintenance. What is common to most is that they live a hard life. They are started cold and run hard with no warm-up. The millage can be misleading because some engines don't run up miles while they are pumping. The miles they are driven are mostly in town (read lots of stop and go). You got to admit they are cool.
Novel but not practical. Don't always assume that the firetruck will be well maintained. The users are firefighters not mechanics. The military chassis would ride so rough that it would shake an RV to pieces in short order.