18SF tank size

[Water Rat]

I would highly recommend Eric Kent at KentFab; I believe they are now in Pembroke, MA.
Very high quality work and a nice guy to do business with on top of that. Good luck with the project.

[GodsReel]

If you plan to go with new motor technology ,you won't need extra capacity. I would use it for storage,or move tank forward to counter the added weight of 4 stroke or maybe a bracket if you are thinking of going that way with it. Food for thought.

[Sceptre20]

I bought a plastic tank at a place in Portmouth RI, I can't think of the name offhand but someone else may chime in.They had many sizes to choose from.
P.S. I will be calling you soon to set up a time to get the footrest to you.I will probably be in Chatham next sunday.