-- Last Updated: Jun-02-13 11:15 PM EST --
If you put the second seat in front of the existing solo seat, especially if it's far enough ahead to allow you to make a decent forward reach when paddling, the boat will be bow-heavy. To make this work, I expect you'll have to move the center seat back, or leave the center seat alone and install TWO additional seats. Still, a boat that's likely to be just 13 feet long overall and barely more than 12 feet long at the waterline is probably a bit cramped and overloaded as a tandem, though less overloaded with two lightweights like you than would be the case with two average-weight people (yeah, the catalog would say it's 13.5 feet, but a Royalex Vagabond is half a foot shorter than specified so I'd expect roughly the same "shrinkage factor" for a Royalex Sandpiper, and my estimated waterline length takes into account Wenonah's highly swept stems).
If you do this, I'd not hold much hope for silicon sealant as an adhesive, but others here will have advice about that. The stock seat probably rests on sheet-metal hangers, and similar ones can be fashioned, stuffed up alongside the hull into the rails and riveted (make slots at existing rivet locations and install more, or drill the old rivets out and re-rivet through the old holes, adding additional ones if necessary). The usual way for hanging a seat would be on wood dowels, bolted end-wise through the rails, but I can't recall if Wenonah rails have enough interior width to allow that. Others here will know. This could end up being the first Tandem Sandpiper ever made.
Pull-Up Strap Handle Kit
Electric Kayak Motor
Canoe / Kayak Anchors
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