I actually organised that "my" tuner tune "my" piggyback (which I don't yet have) to make proper use of a LiLPG setup... no problem, but I didn't receive any discount on the price!
I was told this is because there is no need to tune a liquid injections system as it actually piggybacks off the OEM injectors...
All depends on how many km's you do I guess.
Being that your economy will be shot to hell on E85, it may not actually be more economical over 5 years.
An example (for me - around 720kms/week, mostly highway)
9.3km/L for 98PULP @ $1.45 x (77.4 avg L per week x 52 weeks) = $5837.42 p.a. fuel cost
8.8km/L for Liquid LPG @ $0.55 x (81.8 avg L per week x 52 weeks) = $2339.99 p.a. LPG cost
6.5km/L for E85 @ $0.99 x (110.8 avg L per week x 52 weeks) = $5702.40 p.a E85 cost
That is allowing for 5% for LiLPG economy decrease without a tune and 30% for E85 economy decrease with a tune.
All theory of course.
But going by that, obviously LPG would be the way to go for me and I would make my money back in 2.5 years (I wish I had know that and LiLPG was available 3.5 years ago ).
Whereas E85 ends up costing about the same as PULP.