tubing considerations on E8000 build

Hi All!

So I'm building a super gravel commuter for myself utilizing a Shimano E8000 drive unit and externally mounted battery. Given to fit considerations I'm going to have to mount the battery on the down tube. I'm trying to think through what tubing to spec for the dt that would be robust enough to securely hold the 6+ LB battery and mount and not crack due to the forces from the battery over time. Tube dia for the dt will be 1.5" and my default wisdom is to go 4130 .035" straight gauge.

Couple of things of note...

1. I have yet to order the battery mounts so I dont have a design for the interface between the shimano mounts and the frame outside of copying what I see illustrated in their dealer manuals for STEPs, so there may be opportunity to make gains here.
2. Build notes.., I'm a big guy, north of 230lbs with a long torso and short legs. The front center will be at least 705mm and I'll use a 44mm paragon ht. I have two options for the motor cabinet, the ticycles one and the cast bracket sold on framebuilders supply. Leaning heavily towards the ticycles option.

Anyone have any experience with this question? Opinions are very welcome too!

best. ken