Access hatch for Antifreeze access

As always Marwayne, your mod for this is done with excellence!  I never thought of doing it the way you did this on our 177 although it would be very doable.  As I mentioned I just took some measurements and used my scroll saw to cut an opening above the 3 valves and installed a trap door over the opening.  Lifting the corner of the mattress is no big deal, at least for now while I turn the 3 valves from above.

Nice !. I am sore today from pulling out that mattress, foam and topper to cut the wood, but it will be worth it. I am going to post my other mods this week to help other s out. Post full pics of your 172 if your have them. Looks good!

Yes, I do lift up the corner of the mattress and let it sit on my shoulder while I reach down and turn the 3 valves.  I timed it last month when I did this - 19 seconds from start to finish with the mattress in its original position.  I guess the only difference from what you do is this way there are no screws to fuss with and no 1 x 2's to prop up the mattress AND plywood.  The mattress is much more flexible to lift by itself than having said mattress and plywood (no flex) which would mean you are basically lifting the whole thing to gain access.

I forgot to mention, I use the little harbor freight pancake compressor turned down to 20 pounds. I attach a water hose adapter and a 75cents shutoff from walmart to blow out the lines also.