Restoring the EEC (evaporate emissions control) system won't improve your mileage but will eliminate gas smells. You can use steel brake line all along the side to the canister. 3/16" IIRC You will need the plastic expansion chamber in the trunk and braided hose. If you restore the system in the trunk and all the way back to the canister but stop there you will be venting to the rear and won't smell gas unless in a closed space.
Restoring the rest of the system from the canister to the air cleaner and fan housing will eliminate all the smell and be better for the environment as intended. You must refill the can with activated carbon pellets, not powder. Best place I've found to get it is a hydroponics supply store. Pet stores usually have only powder and very pricey.
There are many threads here on this job. Do a search.
jim
'71 SB(DD only 79K(now 84K miles) & '78 FI Westy (project)
PO of '65 Beetle in '69, '70 Crewcab & '70 Ghia in '77
'71 Super inside rear vents now availablehttp://www.openroad.ca/volkswebbin/view … p?id=85915