Do a search on the Montana LLC. They (the feds & the state) are very aware of illegal LLC's and have cracked down on this and anyone doing it IS under a microscope from the day they set it up. IMHO not something I would want to be under waiting for the second shoe to fall.
There is no statute of limitations on fraud. :W
Seems to me a MUCH simpler way to have done that was to set up the 'so-called' domicile in Florida FIRST, buy the RV and have it registered in Florida AT the dealership and therefore pay the lower Florida tax. Did your friend fake the Florida address too to obtain the DL?