Any ideas on hooking up an ozonator to a 10 year old Marquis 3000-C?

The venturi tube doesn't seem that accessible.

most repair/parts web sites will have some very good instructions on how to accopmlish this procedure. here are several that helped me.
hottubessentials.com
delozone.com
spacare.com
spadepot.com
spapartsnet.com
poolandspa.com

some of these sites will only list parts but they're several that have complete instructions.
you might find that you can do the upgrade using a marrei injector attached to a by pass. i found this to be the way to go.
also a mix degas vessel might be something to consider.
hope this helps....and i hope this posts have been having problems with answering posts laterly