I would try printing with a wide brim, and waaaaaaay slow. After 2/3 of the tubes print stop it and let it cool down, peel it off and see how the bottom looks, the first three layers are the key, that shouldn’t take more than 20 min. If it was what you wanted reprint as set. If not go to a raft, but you will need to sand it.
Tried it and as I thought the bottom was still flat and it was looking more like it was made of flat steel than tubing.

MIght try a raft later and see what happens.