My boat is a 36 footer. When I purchased it four years ago it had no water tanks
though I have the origional plans and it once had aluminium tanks
. Not sure what happened to them.
Two years ago I had two 120 ltr plastic water
tanks made up for me. Because they were fitting against bulkheads and under bunks they were an odd shape. So I drew them up and emailed my plans. The manafacturer quickly made them up to my specs and mailed them back to me. Perfect!
They are strong (7mm) and made from HDPE. White in colour. I got them to put double thickness in one area in the top so I could put in inspection
hatches. HDPE does not affect water taste and the colour helps with discouraging any growth. They were both about $450 each.
I've yet to order another one for the foxall which will be about 200 ltrs I suspect.
Baffles? I'd definately put baffles in it. It's not about the size of the boat, it's about the size of your water tanks. Mine are approximately 1100 long and that's a lot of water and a lot of pressure being made if they are half full in rough seas. So definately baffles.
And make sure you use drinking quality hosing to connect them. Plastic all the way.
I'm in Australia
and just so you can see what I mean, this is the company I used. http://www.abbertanks.com.au/