Hi Jan:
Shouldn't be a problem. If they deny a claim, then they will have to deny the claim of a hobbiest that uses epoxy and welding torches, etc. The only real question that comes up with manufactured homes is if there is a wood stove installed. The only fire that I've heard of regarding a studio is that the woodstove got out of hand or that some one doing raku dropped a piece on the floor that sparked a fire. That was pure carelessness. Should have set the kiln up outside rather than inside the shed then caring the garbage can outside.
The building next door is still part of your property and would be automatically covered on that same policy as an "other structure". Would be safer, of course, to have it away from your living structure, if possible.
Please let me know how it turns out.
Diego