Howdy
@Andrewm02, shhhhhhhhhhhhh.

I haven't mentioned here on the forum Ive put a stupendous
View attachment 33360 diesel heater in our van. Ive kept that to myself
Although our 20.63 is 2014, its the 2013 layout i.e. no slide out like yours I suspect. I ditched it because of the weight, so the heater locale wasn't affected by the slideout.
View attachment 33359
The heater is installed under the couch wing next to the fridge, with the ducts under that seat one facing forward and one towards the back, and ran the cabling up inside the fridge cavity, mounting the controller next to the fridge. They recommend the controller 1500mm off the floor and away from heat, cold or drafts
View attachment 33355 View attachment 33354 View attachment 33356 View attachment 33357
Keep it to yourself
(PS On a serious note its a great spot and works really well. The ducting suits perfectly. The way the ducting routes, slightly more air comes out of the fridge side which is better. I thought mounting the other duct in the corner and not on the end of the couch may be a boo boo, but its turned out well where it is. I can send you some more pics and measurements etc if you need it)