never unless there is a leak, lol.
The gasket will dry in the position and form it is in and should maintain the seal. Tightning it will deform it and could cause a leak, although the road will shake and move the AC unit, so there might be some potential for degradadition.
It is protected from UV rays also, so will not crack like the caulking on the roof and wall outer seams which you should check often, be paraniod about, and completely re-do every 2-3 years or else risk catastrophic water damage to the walls and roof.