I agree with Faiview a tunnel does not have to be fancy. I've seen tunnels made out of chicken wire with carpet material, out of plastic garbage cans. etc. but candidly, I've never been that convinced that it makes that much difference in sound.
One of the major companies (either Yamaha or DW???) made (still makes??) a bass drum extension to place in front of a bass drum for extra low end resonance.
The theory behind a drum tunnel is simply to allow the low frequencies to move some air before recording them (which is different then using something like a blacket to cover the kick drum for isolation).
The reality is, a decent sounding drum that is well tuned and properly mic'd should sound good - if it doesn't sound good, it makes more sense to fix that chain rather than creating yet another variable.