does sealed off really mean sealed off?
8:1 BATTERIES
All batteries must be securely mounted; must be of sufficient capacity to start vehicle at any time. Batteries may not be relocated into the driver or passenger compartments. Rear firewall of .024-inch steel or .032-inch aluminum (including packagetray) required when battery is relocated in trunk.
In lieu of rear firewall, battery may be located in a sealed .024-inch steel, .032-inch aluminum, or NHRA-accepted poly box. If sealed box is used in lieu of rear firewall, box may not be used to secure battery and must be vented outside of body. Relocated battery(s) must be fastened to frame or frame structure with a minimum of two 3/8-inch-diameter bolts. OEM located batteries without complete OEM hold-down hardware must be secured to OEM battery box/tray using the same 3/8-inch-diameter bolt hold-down method described in previous sentence. (J hooks prohibited or must have open end welded shut.) Metal battery hold-down straps mandatory. Strapping tape prohibited. A maximum of two automobile batteries, or 150 pounds combined maximum weight (unless otherwise specified in Class Requirements), is permitted. Maximums may vary according to Class Requirements
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Tanks:
When permitted by class regulations, fuel tanks located outside body and/or frame must be enclosed in a steel tube frame constructed of minimum 1 1/4-inch O.D. x .058 chromoly or .118 mild steel tubing. All fuel tanks must be isolated from the drivers compartment by a firewall, completely sealed to prevent any fuel from entering the drivers compartment. All fuel tanks must have a pressure cap and be vented outside of body. A positive-locking screw-on fuel tank cap is mandatory on all open-bodied cars. Insulated fuel tanks prohibited. When used, fuel cells must have a metal box protecting the part of the fuel cell that is outside of body lines or trunk floor, excluding hose connection area in rear. Non-metallic fuel cells or tanks must be grounded to frame.
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Seam sealer works really well.
The firewall needs to be sealed for the fuel cell, not the battery. If you run the battery and power lines along the floor, good luck getting a positive seal in that area.