Yeah, there aren't a ton of obvious locations. Since it's a track car, why don't you just mount both of them to a home-made metal bracket back by the bumper...maybe using the bumper bracket bolts, or however it is I see the track cars attaching them. They might have to "pull" a little ways, but I think it'd be fine.
I know you said you have a pump but consider maybe selling one and getting a fuel cell module. That’s the route I’m heading.
nss are those sliders i see.