98" is a bit long for a Hobie 16. The stock extension is about 80", maybe a bit longer.
Note that anything over 60" is going to incur an additional shipping charge. APS charges $25 extra. Do you trust UPS with a long, skinny, lightweight box?
If you're going with a fixed length extension, you can use the hardware and grip from a stock extension and order raw carbon tube from
http://www.carbonfibertubeshop.com (Item# SM6260F) in 60" lengths and the 5" connection ferrules (Item# SM615FER). 3 lengths and 3 ferrules is good enough for two extensions with no waste. (One ferrule is used to reinforce the connection end - cut in half and inserted until flush with the end.) You just need a bit of epoxy to glue it together.
For about $230 (that includes shipping), you get the materials to make two extensions (you
will eventually break one) that are about 4" longer than the stock extension. They're super lightweight and what many racers are using now.
The elastomer joint on the Ronstan Battlestick is subject to UV degredation (it gets brittle when left in the sun). It's meant to be mounted with screws into the tiller crossbar and does have a disconnect mechanism. My tiller is the first thing that comes off when the boat hits the beach (you can't lay it on the tramp on newer boats and it sticks way out to the side otherwise).