Yikes, I can't imagine going head first into the lazarette.
My technique was to open the starboard lazarette cover, and then using
my arms I would let myself down into the opening until I was standing
the plywood on the top of the fuel tank. Stand their facing the propane
tank on the port side. Just inboard of your feet there will be a
vertical opening maybe a little over a foot high just above the plywood
and below the cockpit sole. You need to get your legs into this opening
-- slowly lower yourself using your arms. You will end up sitting on the
plywood. Then lean backwards and tilt your head to get it under the
outboard fiberglass. You will end up sitting on the plywood with your
back against the inside of the hull. This actually is fairly
comfortable. You may want to use a pillow or two.
To get out of the lazarette, reverse the process.
I am 6' with a long torso, and I did this when I was in my early 70's.
It is wise to have someone there who can get the tools you forgot, can
help you if you get stuck, and can call 911 if you get hurt.
Your arms do need to be strong enough to support much of your body
weight, and they cannot give out half way through this process. If you
can't do 10 pushups (it is OK to cheat by putting your weight on your
knees rather than feet), it may be best to pay a boat worker. Cheaper
than time in the hospital.