I haven't got it completely detailed but I will skin the subframe with a sheet of thin aluminum with a approximately 1 1/2" lip. bring the in and out through the floor in one corner and run tubing on top, haven't decided on what to poor....would really like to use sand, great heat sink and flexible but really heavy. I want the final surface to be something really durable and can rinse out with a hose, like a bed liner or resin, still looking for the right thing. I've seen small diesel powered hydronic heaters that are thermostat controlled so that was my plan in that respect. j
I will try not to get too far off track here, but will instead attempt to share the results of my findings from many hours of research (talking to people about their builds, i.e. real life experience, talking to manufacturers about their products at trade shows and such, reviewing technical data, studies, etc.)
If I were NOT going to use a Vacuum Insulated Panel to build a box or were looking for something a bit more DIY friendly, I would construct a box as follows:
16-20 gauge aluminum sheet glued to polyisocyanurate foam sheet (1.5" thick), glued to 1/16th inch bamboo veneer interior paneling. "Cut outs" can be left for doors and windows, though I would not have any windows that open and only 1-2 windows, likely clerestory for whole camper (assuming small box, like something for the back of an FG)
The exterior of the box, upon completion, would be sprayed with 1/8th inch (each) of Lizard Skin heat and sound insulation. When I am inside, I dont want to hear the outside (people talking, music, dogs, kids, car doors, ATV's, whatever). If I do want to hear the outside, the door is never more than a few feet away. I could care less about cross ventilation for HVAC. (see door example above if desired) The spray seal and laminated/layered paneling creates a sort of "monolithic" cube structure: no seams to leak, no thermal bridging through window frames, no skylights or vents to leak, etc. Nothing at all on the roof or penetrating exterior walls for the same reasons. Clerestory windows would be 2-3 pane with interior blinds/shades for light control. Lizard Skin would be spray over window and door flanges for proper weather sealing and to eliminate thermal bridging.
Now you have a sealed box that can't "leak" heat or sound, in either direction (from the inside out or vice versa). Panels are glued using 3M 78, 90 or 92 series sprays, which do not harm the polyiso foam (about R-7 per inch) and will stick to almost anything. Foam and interior panels can be oriented and laminated in such a way so as to avoid continuous seams, like laying bricks. Once everything is laminated together and sprayed with Lizard Skin, you have a VERY rigid and solid box with only one opening for a door. This goes a long way in making a solid structure, reducing vibration, sound transmission, etc.
From a DIY standpoint, the glue and Lizard Skin can be sprayed DIY or professionally, there is no welding to do on the panels, foam, sheet metal and your favourite interior paneling can be sourced almost any where. All materials chosen are easy to work with: no messy fiberglass work, nasty chemicals, hours of sanding, tubes of Sika to dispose of, etc. The Lizard Skin does not have an R value according to their tech dept, but does have a K value, which is the inverse of R value if I recall correctly. The layers of spray, panel, foam, etc., basically act together to "block" almost all heat and sound. It is reflected back to where it came from, just as it would be if one were to use a vacuum insulated panel. Nothing gets through the vacuum and I am attempting to achieve the same thing with simpler/cheaper DIY technology.
A bonus of this construction method is that HVAC demands are almost non-existent. You could easily heat a small box with a catalytic heater, a mini fireplace, small electric space heater, etc. For A/C, you have fewer options, though I did find a few companies who make miniature air conditioning units. If you were able to avoid hot/humid climates, you may be able to get away with small fans inside or a screen in your door if that meets your needs. I would mount the HVAC under the living space like an OTR truck box for several reasons. The weight is carried down low and not up on the roof where it changes vehicle dynamics or could be damaged by limbs, etc.. It is easier to service there and keeps the penetrations into the living space at the floor level where rain, dust, etc. are less likely to intrude.
Hope that helps some.
