On my last 2 models I haven't used a UAT (or similar).

One uses a felt clunk in a one litre tank (Wren 44) & the other BVM Sabre
(P-60) uses a small fuel tank (2 oz I think) with the pick up tube fixed in the middle
of the tank, after the normal kevlar tank.

You could probably squeeze a similar small tank crossways in front of your 4 existing. - John.