FWIW, we were able to successfully install grommets on a tramp while it was still on the boat.
First we reduced tension on the tramp so it wouldn't rip (might not be necessary, but wanted to be safe).
Sewing the reinforcement patch was a bit of a PITA. It was a two-person job. We had to put the boat on the side and used a sewing awl from one side while the guy on the other side fed in the line for the lock stitches. A very low-tech but cheap and effective sewing machine. Awl kits can easily be found on eBay or specialists such as Sailrite ( link here
). Use some high-grade polyester thread for durability.
Next step was to build up a solid base under the tramp to support the die so it was pressing up slightly against the tramp - couple concrete blocks and a chunk of 2x4 or two did the trick. Solid hit with the punch and the hole was done. Inserted the grommet halves into the die and punch and then sealed them home.
Took us about 90 minutes the first time (about 70 of it screwing around with the reinforcement patch. I'd guess we could do it in 30-40 minutes if we had to do it again). Setting the grommet itself was quick and painless.
If the awl is $15 including shipping and the grommet kit another $20, it seems to me to be an approachable DIY job.