serious answer to a serious question: to properly insulate your bus (for sound/warmth) you need to start from scratch...a bare bus. tank the underside with a heavy underseal install dynamat or similar to cover approx 20% of each panel (doors, side walls, arches, bulkheads, cargo deck, firewall etc etc.) Replace the woefully inadequate sound proofing above the engine bay with a lead sandwich (code 4 lead sandwiched between two sheets of 20 mm closed cell foam) install rock wool (bagged) around the (dynamatted) fuel tank tank the inside panels and floor with rust preventative paint (epoxy or similar) install 12mm closed cell foam lining behind the trim panels. install a sealed vapour barrier between closed cell foam and trim panels 20mm closed cell or Jute underlay on the floor 9mm ply over this reflective (Foil faced) laminate underlay over this Carpet over this Ensure all seals are good Pop top headliner needs to be removed and either polystyrene or rock wool (bagged) between roof and hardboard liner reflective scrim (foil facing the roof side) installed before insulation That's without treating any box sections It's a big job to do it properly and replace crappy pancake filter (if fitted) with original air filter box to reduce induction noise
only if you bag it so that moisture cannot infiltrate....Closed cell foam is better but will also require a vapour barrier between the foam and the trim panels rock wool is good for heat insulation but only attenuates higher frequencies....closed cell foam will provide similar heat insulation and reduce a wider range of frequencies if you're going to the trouble...kill two birds with one stone. Do dynamat the metal panels also....it's an hour of a job and worth the cost
Basically...what happens when you insulate a structure, you're raising the temperature sufficiently to absorb more water vapour in the atmosphere...this vapour will condense on any surface colder than the surrounding surfaces, hence the need to install a vapour barrier...otherwise, you are simply increasing the levels of condensation another worthwhile accessory which i've rarely seen fitted to buses is a ceiling fan...heat rises
Basically, just stick a bit of lead flashing to the centre of each panel (does the same as dyna-mat but cheaper), then stick the foil-backed bubble wrap to each panel and call it a job. Happy days.
