Ecotemp L5

I had originally planned on going with this water heater since it only requires batteries. I was going to mount it on the nose close to the propane tanks and plumb it into the water system. I didn't notice where they say not to permanently install this until recently. Is that just something they have to say for liability reasons? I seem to have seen more than 1 person use one of these in a permanent setting. If this is the case how would one go about setting up the plumbing to make it easy to set this up when needed? Thanks in advance.