1) How bout installing floor or ceiling venting in the TM for AC/furnace airflow? The rear section of TM's are an entirely different climate zone from the "living room/kitchen area", especially in the longer models. it's done in the "big rigs" and even 5th wheelers, so why not a TM? It could solve heating issues in the bath and temperature control in the rear.
2) Install additional insulation in the rear storage compartment between the compartment back and the bathtub. Cold weather camping is very chilly when you rear end freezes
from contact with the icy toilet seat, especially as there is no heat available (and no place to put a heater, either!) in the bathroom. Additionally, suggest to Thetford to produce a "heated seat" after market option on their product.