I have never seen any kind of portable unit.

The H-100 will go through gas like a monster - so propane bottles won't be very useful unless you have a dozen or so lying around and don't mind hauling them back and forth to the store.

I'd suggest an permanent installation of a H-100 or H-250 (depending on the size of your pool) with Natural Gas (if you have service) or Propane and a large tank on site. You only have to use it when you need heat.

I have an H-250 (the less efficient model - not induced draft) on my 22000 gallon IG. I only use it 'when I want heat' like early in the season, or late in the season. The rest of the time it is powered off.

I think you will find that working a method to hook and unhook a portable unit (that you will likely have modify to be portable) will be more hassel than having a permanent install.