Re: Dpa 4099
The DPA is good for bodies up to 55mm deep with the standard violin/mandolin clamp. With the sound hole placement on the Tacoma it might be worth trying one before purchasing to ensure you can get a sound you are happy with without getting in your way. I would thing up near the scroll toward the sound hole or on the lower bout toward the bridge would be good starting points, though with no lower f-hole near this position it may end up with too much body.
You should be able to get longer pieces to extreme the depth of you radius clamp from a violin dealer/repairer. Not sure what length the chin rest clamp bits for viola would extend to though.
Hereby & forthwith, any instrument with an odd number of strings shall be considered broken. With regard to mix levels, usually the best approach is treating the mandolin the same as a cowbell.