I finally got a call back from 'Nathaniel' at Forest River this morning. He had much better descriptions of what is available for my pontoon from the manufacturer
I asked for part numbers and he told me that they don't specifically keep part numbers for external use as they like to rebadge them for each year, but that my local dealership would be able to get the current name and estimate shipping for the following items.
$190 Strakes (inside of outer tubes only)
$500 Performance Underskinning
$1200-1500 3/4 length Sport Tube (ends in front of the original transom)
$1000 to ship (crated/shipped wire fee, estimated)
$1800-2200 Full length triple tube (22ft)
$90/each plywood (4x8.5) for new decking (6-7 required)
$7-8/ft side deck rail
$1200/per tube replacement of the original pontoon tubes. ($2400)
So here is what he told me,
The Sport Tube will not replace my current transom, it will not increase the hull rating for HP, if the proper paperwork was done it could potentially increase my weight/person capacity, it is a bolt on affair. The Sport tube does not have lifting strakes, nor do they make a kit for adding them, nor does it move the gas tank to the center tube, nor does it have any 'in-tube storage' for skis/etc. I would do the lifting strakes on the outers, the underskinning, and the sport tube if I went this route. Roughly $2200 (plus shipping)
The full tube is like the one toonguy posted on another thread, where the cross braces for the front and rear are pre-welded at the factory and would require me to redo the decking.
Picture of ToonGuy's project tube

- tritoon_tube.jpg (71.86 KiB) Viewed 4341 times
Which is why I also included the pricing for plywood and side molding. I also got prices for new replacements of the outer tubes because if I went this way, I might want to 'upgrade' to a 25ft deck to get more front porch area or a rear swim deck area, which would also require some rewiring and most likely new control and steering cables.
plus
decking (7 * $90 = $630)
and
side moulding ($8/ft * 67ft = $536) plus materials (screws, glues, flooring -- $unknown)
New center tube ($2200), new outer tubes ($2400), underskin ($500), lifting strakes ($190) = $5100 + $630 + $536 = $5730
(minus $2400 if I reuse my current tubes = $3330)
I was hoping the new center tube would be a bolt in affair with a few bolts that were just a pain to install, but being that it is a full tube with cross braces built in that would require a new deck to be constructed on top of that, a factory full tube just doesn't seem like it would be feasible or justifyable. At this point if I want factory only equipment, it looks like the sport tube is my only option. What I don't like about it, is that I was really hoping to add more floatation to the REAR 1/3rd of the boat, not the front 3/4s of it.
I think it is time to 'sit on this one' for a while, save some pennies and keep an eye open for a bolt in aftermarket third toon or suck it up and buy the Sport Tube.
I also in quired about a I/O tube, he recommended against it (hard to work on and about $1500-2000 additional over the outboard full tube) and let me know that Forest River no longer sells any boats with 'Through Hull' exhaust, if I want that I will have to buy a boat that is about 2 years old.
-ron