You can go as deep as you want (1/4" valleys ?) but the question is do you really want to.
Cabosil doesn't wet out clear and it will definitely kill the 'stripper' looks. Sanding this stuff may also spoil your taste for your wood strip kayak project.

If you need to fill, identify the low spots and use plain epoxy (Raka is perfect for this because it is very clear) and loosely imbed one or two patches of light 4oz.fiberglass into it. The fiberglass will float, traping thick layers of epoxy under it. The fixup may turn out reasonably clear and the sanding will also be much more pleasant. In fact, before the epoxy completely hardens (and you will have plenty of time with the slow hardener), use a sharp furniture scraper and shave off what you need from the surface. The epoxy will be like hard rubber for up to a few days and it shaves off perfectly at this stage. You will need to refill again (maybe few times) to get a reasonably fair surface. I would also try a belsander (50grit) at a later stage when the epoxy is hard enough so that it will not gum up the belt.
The filled areas will need to be as horizontal as possible and you may want to add masking tape 'dam' so that the stuff doesn't run off.
Good luck with this.

Vaclav

: I am finishing up my first stripper canoe as practice before I build a sea
: kayak. One problem that I have is that there is un-eveness in the hull
: (bumps and valleys), this is after sanding. My question is, How deep can I
: go with using epoxy and cabosil mixture to fill the valleys? I don't want
: to keep sanding as I am getting thin in some areas. I am using RAKA with
: the non-blushing mix. Thanks in advance for the help.