I'm lucky, I have a tree growing behind my side driveway, So I put landscape timbers (6 x 6) under the keel with some 2 x 4's on the ends in the back, tie a rope to the tree and the transom eyebolts and slowly pull the trailer out until I can put more timbers under the front after the trailer has passed that spot, then I just pull the trailer out the rest of the way. I like using the timbers cause they are big, massive things that will not shift on me. This way I can work on the trailer without the boat being in the way. As a safety rule, (and I know that some here will probably disagree with me) I NEVER go under a boat that is on blocks. It only takes one mistake to have the thing fall on you and crush you to death. If I'm painting a hull I use a roller on a ceiling stick to reach under the hull. For all other things I wait till it's back on the trailer, then I'll crawl under. If a crossmember is in the way I just shift the boat forward or backward as necessary on the trailer.
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1987 V20 w/1987 150HP Yamaha on a Shoreland'r Trailer
1978 16.5 Airslot w/1996 120HP Force on a Four Winns trailer
1996 V21 w/1993 200HP Mercury on a Shoreline Trailer
All towed by a 5.7L Hemi Durango.
If God didn't have a purpose for us we wouldn't be here, so
Live simply, Love generously, Care deeply, Speak kindly.
(Leave the rest to God) 
Silence, in the face of evil, is itself evil. Not to speak is to speak, not to act is to act. God will not hold us guiltless.
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