lots of good info jammer,
the o.p. is clearly enthusiastic about trying this but i don't see these 3 relevant premises explained well here...
1. why specifically use radiant IN a 'stream?
2. careful cost comparisons of available rv heating systems.
3. an objective list of all the + and - of each approach to heating a travel trailer.
of course ALL that was requested was heat loss calculations, not an open debate on the nature of this project.
so there is NO need to address these issues...
but its pretty clear the heat loss calcs are a crap shoot disguised with math.
both hiho and now u have suggested the better way is to calculate how many btus are needed to heat a 31 foot 70s trailer.
to do that NOW the o.p. needs someone with a similar unit to step up, since the target trailer is in construction mode
i still think there will be significant heat loss via the frame/ribs/shell UNLESS this is accounted for in the design.
from an earlier post it appears the o.p. has used a felt layer between the ribs and INNER skin,
my understanding is that this will enhance heat conduction/loss to the outside, not hinder it.
yes 2 1500
w (~4-5k btu) electric space heaters will do the job nicely in MOST pacific northwest weather...
and 3x5000 btus heaters would be toasty inside a 31,
except in the mountains or EAST of the cascades or during one of the common deep cold snaps that happen or during WINDY conditions.
i can confirm that 2 vented cats of ~6-7k btu will keep this size unit VERY toasty, down the upper 20s...
because most of the plumbing is INSIDE the unit, pipes are protected...
but the tanks are NOT warmed with space heaters so to deal with freezing tanks they DO need heat.
and the water tanks are NOT rigidly attached in the subframe, so the heating needs to allow for shifting,
unless the tanks are better fixed.
the forced air ducting warms the holding tanks slightly, with very little weight or highly technical design.
cats and furnace both run on propane the most common fuel source for most of rv doodads...
i like the outside the box thinking/approach that one of our canadian member smokeless joe took with an ALL DIESEL system...
amazing work in that thread some brilliant design and beautiful appliances...
but i'm not sure the unit has every been road tested/used even after 3-4 years.
as a last curiosity/aside MANY of the newer classics DO HAVE radiant heating in a very small section of the floor.
most of the pumping is on the street side in the newer classics, except the water pump, which is curbside along with the furnace and water heater.
this means a heater duct crosses UNDER the floor to curbside and pex water pipes cross over/back to the pump.
so IF i stand in just the right spot (where the floor vibrates) i can feel the warmth...
ok, maybe not.