Pertaining to using propane for drying, here's a couple of previous threads on it that you might find interesting:
Propane dryer in a motorhome
Gas dryer OKAY?
Check Bob's post in the first thread about the regulations where fuel-burning dryers must have air coming from the outside (or click here
to go directly to his post). Not only does that make installation more impractical but using propane to dry doesn't make sense from an efficiency standpoint for me.
We use a Splendide combo that is vented to the outside and we're happy with it and we've been full-timing for quite a few years now. A stackable might be nice but for us and the amount of laundry we do, we're happy with the combo. But that's just us ...many use stackables in motorhomes and love them.
If you plan on doing a lot of laundry, then perhaps a stackable would meet your needs better. However, remember it's going to weigh more and take more space. For us, we hand wash a lot of stuff and don't use sheets (we use cheap sleeping bags zipped together and blankets. We air out the sleeping bags once a week and spray them with some freshener and disinfectant. We throw them out or donate them after a few months (some homeless shelters will take gently used and clean sleeping bags and ours are both) and we'll then use new ones. We've followed that pattern for years.