Bolt-on fuel bags?

Yes.

Yes +1. If you use a top tube bag, which I do on all my bikes, so much more stable bolted.

I will, it's for bikepacking purposes

Not much choice on the market however.

Yes, include them.

I use one of Apidura bags. So much more stable bolted.

Not much choice of what frames or bags? My Topstone has TT bolts. I just by cheap Rock Bros TT bag (also sold as west biking) as it has a stiffened base, drill a hole and put a washer under the bolt. Perfectly good enough for me.

https://www.amazon.co.uk/ROCKBROS-Waterproof-Triangle-Pannier-Cycling/dp/B07Z4T8M7X/ref=mp_s_a_1_1_sspa?crid=EC3ZXAQWA20H&keywords=bike+top+tube+bag&qid=1660729805&sprefix=bike+tip+tube+%2Caps%2C154&sr=8-1-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUEzQU5IU0lMRDJVQ1pCJmVuY3J5cHRlZElkPUEwMDk0OTM0MjYxNkVOS0ZGUDZRUSZlbmNyeXB0ZWRBZElkPUEwNTU4NDQ4MVFBME9MNkwxTkpSMCZ3aWRnZXROYW1lPXNwX3Bob25lX3NlYXJjaF9hdGYmYWN0aW9uPWNsaWNrUmVkaXJlY3QmZG9Ob3RMb2dDbGljaz10cnVl

I have a couple of old AlpKit ones, but they can be quite floppy unless you pack them carefully. Not sure about their current versions.

I have the Restrap one - very secure, big enough for my + size phone and doesn’t damage the paintwork

Yes. We use Restrap bags. Mine has the strap (non bolt) version, my wife’s uses the bolt version and is more stable. The bolt on internal frame bags would probably require a custom bag as the Niner one was a bad fit on the Niner frame and was sent back

I've found a nice one from Bontranger also

Thanks I'm going with bolts then

Yes. I'd put them on any custom frame, personally. Have a Restrap strap-on one (oooo... matron) which I put on any bike when it's going to be useful... including the full-sus... would rather it was a bolt on.

76 projects make a neat one that slides on to the bolt on mount. They even do a stick on mount if you don't have top tube threaded holes on the top tube

Mounts are great especially with the A.S.S. system or even if you don't have mounts
https://ukgravelco.com/76-projects-a-s-s-anti-strap-system/