I'm glad to have heard from you. It had been about 4 days since your last post and I was kind of concerned that you may be frozen to the ground under your RV ROFLMAO At any rate, good to know that you're making some progress, even if it is slow going.
As for the pipe foam along the slides, if you can pull in your slide about an inch and lay the pipe foam along the walls and ceiling, then extend the slide again and it should seal much better than what you have from the factory.
We also have a rear wall that's all window and two pretty large windows, one on each side so I know exactly what you're facing with cold in that area. You may want to just tape a piece of that pink foam on the big window from outside and keep the plastic in place on the side windows. That may help a little more if you don't need that much light during the day.
As for the RV and the furnace, realize that you're facing an uphill battle trying to replace the heat lost in your RV with a 30,ooo BTU furnace. Realistically, you're losing 35 or 40 thousand BTU's and the furnace just can't keep up. The skirting, insulating the big windows, sealing the slides and keeping the heat loss to a minimum by not opening doors any more than needed is about all you can do, but hang in there, hopefully the cold will break and you'll have a few days of warmer (near freezing) weather in the next week or so.
Glad you're not stuck to the ground under your RV, keep us posted
