Hi Tom, I assume you are talking about glassing the outside of the hull for strength and protection. If you have finished your DUKW with all the strakes and other details on the hull I would think twice about trying to glass it as it will be difficult to get the cloth to conform to all the nooks and crannies. However, if your hull still has flat sides and bottom then it will be pretty straightforward to glass it. I used materials from
www.easycomposites.co.uk and am very happy with their products. I used 100 gm per sq metre cloth and did not thin the epoxy (which many recommend). There are some pictures of the process on my Chris Craft build log (click on the link at the bottom of this message). The Chris Craft was my first attempt at glassing a hull and it went more smoothly than I feared. It gives you a hull that has a smooth finish for painting, pretty well guaranteed waterproof and it's very unlikely that you will get separation of the panels.
And in case you are confused about terminology, you do not want glass fibre mat, which is a random assembly of short fibres. You want woven cloth, which you can smooth over your hull before applying the resin. Steer clear of the Halfords glass fibre repair kit!
Greg