Another option, a variation that i have used is to support a pole from the rafters. Suspend the hammock from the pole ends.

Two major benefits: The the forces on the rafters are straight down and not laterally. In addition the forces on the pole are determined by how many anchor, or suspension, points you have as the weight of the hammock system and suspendee are divided by the number of hang points. I ran a pole, a long stick of lumber would do, across the garage truss chord and suspended a 'ridge pole' from the stick in the bottom chord of the trusses.

Personally, I use a very portable hammock frame that I can scoot around and into or out of position easily. But it doesn't look like you have much room for a portable frame. Therefore, the advantage of a suspended ridge pole is you can undo one end of the hammock and stow it out of the way.