+2
From the Fender site info, it looks like you can unplug your combos internal speaker and connect a standard 1/4" speaker cable directly to the combos amp section. So you could easily give it a quick try with a bass cab to see how it does.
Your combos internal speaker is rated at 4 ohm, so using a 4 ohm bass cab would be the safest choice for use with your combos amp section.
With a 5 watt tube amp, I'd be pretty much expecting very low clean volume levels, but it might just end up making a very cool sounding low volume fuzz-bass rig for ya.
(if your bass cab has a level control for the tweeter, you may find turning it down or preferably off may end up sounding best)