Try and put your EW bets at a bookie other than Betfred, Coral, William Hill, Ladbrokes. Those 4 'big' bookmakers only pay out on the 1st 4 to finish.
Most others pay on the 1st 5 horses home whilst Bet Victor pay out on the 1st 6 horses.
Open an online account if you can. Just don't give your cash to the 4 bookies listed above. They're out to fleece the once a year punters every time the National is run.