Oh - I built my livewell from 3/16" PVC board from US Plastics Corp. with a PVC angle lining all the corners and a PVC 3/4" barbed bulkhead fitting for the drain. Pricier than a rubermaid tub, but higher quality too...I sprayed expanding foam insulation around it once it was installed. (Not closed cell I know but good enough to neatly insulate the live well from the summer sun.) Before spraying the insulation I capped the drain channels (stamped into the bottom of the boat) with aluminum flashing so they would still drain the front and not get clogged with insulation. To install I sliced a hole in the top of the middle bench seat with my rotary cutter and cut the rest out with a pair of tin snips - using the rotary to get each of the 4 cuts started (rotary cut a slice at each corner, tin snip to the next corner.) I had a very cleanly shaped cutout and retained the structural support of the bench seat. I have just enough material to rivet to on the topside of the bench both forward and rearward of the livewell. My livewell measures 15.5" x 8.25" x 36" which is approx 2.75 cu ft or ~20.5 gallons. Not tournament sized (usually 32 gal min) but good enough to resuscitate a worthy opponent after a good fight or keep a few for bragging pictures later. It's a livewell in a 1436 jon boat, I can't be too picky. You'll be able to go wider in a 1448, so you'll need an extra 2' x 4' sheet but you'll get just over 27 gallons if you keep roughly the same dimensions & add a foot in length.
3 sheets of 3/16" thick (2' x 4' sheets to save on shipping)
https://www.usplastic.com/catalog/item.aspx?itemid=23056
Angle (enough to reinforce all corners - I used 1/8" x 1" x 1")
https://www.usplastic.com/catalog/item.aspx?itemid=23195&catid=733
Bulkhead fitting for the drain - the rest of the threaded plumbing can be sourced from Lowes or HomeDepot
https://www.usplastic.com/catalog/item.aspx?itemid=46177&catid=477&clickid=searchresults
