Well, I have some good old B+ mods to make your funky TL less so...It only took me 9+ years to quit griping and do something about all the cabover lumber clunking and other squeaking and rustling sounds on anything but a smooth road. The incentive was that in the hot months until October, our monthly RV runs are just to a restaurant or local day-use park to walk dogs somewhere different. State parks w/ one or two overnite stays are for cooler months rest of year.
After 2 full days, we MAY have a quiet(er) MH. I removed our custom cabinet 3-sided shell (where big TV was) and organized some excess wires. Tried to access headliner from coach by removing green plastic trim from rear edge of curved plywood deck of overcab cabinets - no way it would come off w/o unglueing it. Could only peel back either end after I took buttons off green vinyl 'flanking walls' and loosened its top 5 or so screws. Put it all back w/ no action taken.
Took out center cabinet frame for 1st time - the custom 3-sided shell removes for access to cabover wiring w/o taking this center frame/TV tray off. Found side cabinets were not secured to white vinyl covered 3/8" pressboard sheet ceiling - no screws, ceiling lifted up freely above cabinets. Added a block of wood to both cabinete to have enough area to sink a screw down thru ceiling pressboard and into cabinet top - SUPER stiffening effect on 3/4 plywood overcab deck. Deck is not secured along its front edge - it merely lays atop bottom of figerglass cabover cap.
Figured out how to get domelite off headliner, drilled a hole right in the center of the plywood deck right thru the sheet metal that is the Chevy cab roof and hidden by cab headliner. Put a screwhead bolt thru it from top and held nut via a wrench thru domelite opening and tightened that sucker down. Used a 1/8" thick 3"x1" steel plate big spreader washer to grab more metal roof. This added more stiffness, tied plywood deck down, and will reduce squeaking due to roof sheet metal.
Glued and screwed a 1x3 by 5' stiffener flat atop along front edge of plywood deck, put it all back together, and hope it all makes a big difference on next outing. Will let y'all know.
Sure feels good to have finally tried to address this.