Homemade dolly + floor jack + jack extensions

Assembled with extension for lifting bow

Here the floor jack is being used with the extension for lifting the stern.

The floor jack was used to lift the stern, then a tow strap was put under the stern with each end of the tow strap attached to a ratchet strap suspended with chain from the ceiling. Then the same was done to the bow. Now the trailer can be pulled out form under the boat.
Although the floor jack was used to do the lifting, I discovered that I can lift or lower the boat simply by using the ratchet handles alone.

Trailer removed and jack stands in high position with initial blocking under keel

Jack stand and adapters

Jack stand with keel adapter in place

After the bottom of the hull was repaired I lowered the boat and supported it in three locations while I applied bottom paint.

Bottom work is finished and the boat is now supported in six locations. Note the yellow ratchet strap and orange recovery strap hanging to the right.

I used four ratchet straps and two recovery straps to hang the boat. The ratchet straps are attached to chain that's bolted to ceiling beams. The ratchets can be used to raise or lower the boat to reposition jack stands, or remove or replace the trailer.

These are a bargain at $10 each from Home Depot. I use four total.

These were $34 each from Amazon, but this particular brand I see is not currently available. I use one at the stern and one at the bow.