Gattonero wrote:A local framebuilder can add two bosses in most cases, on a steel frame is relatively a quick job and would involve repainting an area about 20cm of tubing.
If in need to carry lots of water, I would however think of an alternative solution, like a small frame bag on the top tube, so to keep an hydration bladder. This way only one water bottle is needed, to be refilled from the bladder. Foam (or spare clothing) can be used around the bladder to keep the water at cool temperature in the summer.
Lots of people are doing so in Bikepacking.
Thanks gatto, you have confirmed the hassle repainting.
Please note this is for a fuel bottle.