I believe that I found a typo in this mod.
While playing through career, and in the early-mid game, I realized that for some reason the FL-T800 fuel tank was mysteriously not showing up in the VAB/SPH, and for some reason was not showing up anywhere in the tech tree in R&D.
I think I tracked it down. In "SensibleTechTree Parts.cfg", there appears to be a very minor typo:
@PART[fuelTankSmallFlat|fuelTankSmall|fuelTank|sasModule|linearRcs|fuelTank_Long|liquidEngine3|liquidEngine|radialRCSTank]
{
@TechRequired = controllableRockets
}
However, when digging through Squad's Parts folder, I find the following in "fuelTankT800.cfg":
PART
{
name = fuelTank_long
...
After changing "fuelTank_Long" in "SensibleTechTree Parts.cfg" to "fuelTank_long", the FL-T800 fuel tank now shows up in the correct node in R&D and is avaliable in the parts list in the VAB/SPH.