I am going to attempt some cockpit modifications to my first boat (had it about 8-9 months). I have a plastic CD Sirocco and want to add some heel & thigh padding which should not be too difficult. However, I also would like to add some additional surface forward of the seat support on each side of the cockpit to mount my adjustable hip pads a bit more forward than the seat housing allows. (I have adjustable hip pads I like that velcro/strap into place but the seat housing is a bit too far back for where I need the hip pads mounted.) I am going to make a pattern and cut out minicell foam blocks then contour them to the inside of the boat. My question is how best to glue them in? Contact cement was recommended and appears to be the favorite from what I have read in the archives, but this job may require some moving and adjusting of the formed minicell blocks to get them in just the right position before they become permanently bonded to the boat. I do not see how contact cement will allow me to do that. Any tips on how to best use contact cement in this type of application or suggestions for a good alternative adhesive?
Use Duct Tape
first to hold the foam in place for testing and getting the proper feel. Then mark the spot and use contact cement. That cement will hold the foam in place for along time. Every so often you may have to use a popsicle stick to squeeze in between the foam and fiberglass to restick.
sing
How difficult to undo?
I was wondering how hard it will/would be to remove minicell after glued in with contact cement…like before reselling the yak? Would
it leave a mess?
Is there a good “temporary” glue/adhesive for minicell to fiberglass?
Removing foam
It’s a bit of a pain to remove, but not impossible. I did it recently to remove permanently glued hip pads so I could install vercro-mounted pads.
I basically cut the foam as deeply as I could with a sharp knife. Then scraped, dug, grabbed, rubbed, whatevered the rest off as best I could taking care not to injure the underlying surface (much). I finished up with some laquer thinner to get the last patches of glue/foam and clean everything up. It occurred to me later that I might have tried to soak it with thinner after cutting and before scraping, so I don’t know if that would help.
You’re right about contact cement
As the name implies, it adheres on contact and no adjustment is possible. You might want to consider using a diffent adhesive. Lexel and the GOOP products are good alternatives that stick to plastic boats reasonably well (as well as contact cement does). These are applied to the boat and the piece being glued, then assembled immediately. They allow plenty of open time for adjustments. BTW, I find that thinning GOOP with toluene or MEK makes it easier to spread and reduces the curing time.
Try Velcro !! 
... My local hardware store sells 2" wide industrial strength Velcro in rolls. This stuff REALLY HOLDS!
... You could use contact cement to hold one side of the velcro to the inside of the hull, and glue the other side to the minicell foam.
.. You will then be able to reposition it to where it fits you the best.
.... Glue the back of the furry side against the hull, so if you ever want to sell the boat, it won't look as badly as the hooked side. You will be able to remove your blocks, and just leave the furry side of the velcro right where you glued it. Just first do a nice looking installation of the furry side, so it looks ok as it is.
Happy Paddling!!
Velcro is not so hot in kayaks
I’ve used Industrial Strength Velcro in several boats, all with the same result. If it’s under any tension, it eventually comes off. This is especially true with plastic boats. The wetter the area, the faster it fails. I’ve also found that the adhesive on it loses its grip in cold weather. When removing Velcro-ed in pads, more times than not, the adhesive fails before the Velcro separates. Sometimes the adhesive comes off the Velcro, rather than the boat or pad. It invariably comes off the hook side, which is molded plastic that’s hard to glue to (it appears to be either polyethylene or polypropylene). Contact cement holds it marginally better, but it still won’t hold up to much tension.
I no longer bother with Velcro in kayaks, except for an occasional temporary test. If I need to install pads, I glue them in.