It's not normally the kind of bet I use Joleg, and 8/1 feels a bit stingy given he'll probably run at least four times. If I were to consider an unbeaten bet I think I'd prefer it with a hurdler rather than a novice chaser anyway.
I think there are only two things that get Envoi Allen beaten this season and that's an injury or a bad mistake/fall. Shishkin similar. They stay fit and stand up they are the best two long range bets of the Festival. Both will halve in odds after their seasonal debuts, and then trade at evens or odds on after winning around Christmas. Aside from Easysland every other bet anyone has in their books area bigger price for a reason.
Compare the Champion Hurdle market for example. Epatante at 4's with shades of 7/2, Goschen 9/2 and as low as 4's and Abracadabras 6's and 7's. Do you really want to be backing any of those ahead of Envoi Allen, Shishkin and Easysland who are an absolute must max stake trixie (sepearate doubles and treble), to have in your book.
It still comes back to adequate cover for Envoi Allen going to the RSA though. Having reflected though I think the answer has been staring me in the face. Any more bets for him must be 'any race' multiples, and I can cover the RSA in a single during the season if there's any inkling he goes that way.