Of course, it is possible to build portable tube amplifiers, but they are less practical for this purpose than solid state (higher supply voltage requirement - DC-DC conversion or a lot of 9V batteries, larger size, fragile, etc.). In any case, only the OP can tell what the intended use really is.
Did try the Continental V2 from ALO and yes have to say it was less than gutsy and dynamic sounding,
it uses a Raytheon 6111 NOS tube.
Go Vibe Portatube is no powerhouse either.