4-6 will get you a marginal unit that probably has issues, especially in the NE. Very few owners keep their units inside during the off season (like I do, mine resides in a heated garage all winter), so outside storage over time takes it's tool on the unit.
The older the unit becomes, the less particular owners become at seal maintenance, so older units tend to have intrusion issues.
Any unit you do look at, lift the mattress and look carefully in the lower front where the walls transition to the cabin over sheet for leakage and / or black stains, a sure sign of intrusion. Look in the cabinets at floor level and the wall to floor transition, again for stains. Sight down the Filon side for ripples that indicate delamination from intrusion and look at the floor covering for lifting or bubbles, a sign of intrusion as well and check the outside for soft spots, all indicative of bad things underneath.
All can be done without disturbing anything and irritating the owner and above all, take anything they state with a grain of salt.
I'd be looking for a unit kept inside in the off season, not stored in the backyard, but youe chances of finding that for less than 4K are slim and none...
But you may get lucky.
Good luck.
