You most likely will get hong
gan by the RPs over there, or worse, get gunned down
(just kidding).
On a more serious note, most of Seletar Camp has since been fully
open to the public - only a small section of it where the remaining
military facilities are concentrated are still protected (i.e. you
need to have a valid reason and change pass to get in), and this is
where route 103 (but not it's W counterpart) goes into - but I
heard that even that has since been gone, and Seletar Camp is now
completely free-for-all (except for certain areas and industrial
compounds near the airport and the airport runway area itself
though, of course 
). Anyone
serving their NS there can confrim this?
Edit: reading the posts below, it seems like the concentration of
military facilities are still there...
