Vacuum bagging is perfectly possible, but dont do it lightly, read and learn everything you can about it because once you are going that route any mistake costs money. start with small pieces, if you make your own paddles those are good practice pieces.
Vacuum bagging is a little an investment, you need the right materials, and the cheap substitutes are mostly for the stuff that cost less like peelply and breather. You will need a vacuum too, one shopvac will get tired fast on a big thing like an hull, you can rig two of them so that they alternate (need to change the thermal protection from the melting one to the switch kind ones)but one hull is still big so a real vacuum pump is the ideal.
The taping down a plastic sheet wouldnt give any different result than not doing it, if properly used a plastic sheet thermoformed to the hull could help you save some weight giving you a better surface finish when you peel the plastic off but that you dont tape it at all. With a simple plastic sheet and tape youll possibly get the opposite: a surface that will need lots more sanding and filling since youll have tons of creases in the plastic.

Oh and about the peelply, if you want to vacuum bag your hull you pretty much need to use it, sold on it or not.

All in all keeping a light cloth, maybe doubling where needed only, wont give you that much more weight. Be realistic in evaluating if the competition level justifies the extra work and money (that could be put into the rest of the equipment)

And if you will end cold molding your hull thats a sweet way to build it, the plug can be done with a number of stringers doesnt need to be a solid piece, there the vacuum bagging, but you should call it vacuum pressing, can be only for the last layer or not at all and just use staples.

PS: why not invest the money in a wood like paulownia and use thinner strips instead than vacuumbagging? did you consider balsa wood for use in some parts of the hull?

:Hi,
: I am shortly to start building a couple of kayaks for racing/training - an
: Australian-designed TK1 by David Payne, and the Guillemot Mystery. So I'm
: looking to keep the weight low (compared to my C17 that has been
: over-engineered as normal in a first-time build!) - partly by using light
: glass (it won't be getting beached or used in rough conditions with heavy
: loads, just lakes/rivers).

: Another thought I had was vacuum-bagging the hull when 'glassing/epoxying it.
: Has anyone done this? Is it possible and how would/did you set it up?

: My thought was to lay the glass down, epoxy, then cover with plastic sheeting
: that was taped to the strongback. This should squeeze out any excess epoxy
: and let it drop down to the strongback so it won't pool on the boat.

: Any thoughts? I considered it as a friend has a new carbon-fibre kayak and
: when ordered, he could have gotten 2 - 3 kilograms (4-6lbs) weight
: reduction if they bagged it (but added $1000 to the cost!).

: Thanks,
: Darren
: Melbourne, Australia