We used the Fiamma typical 2/3 bike cover on the motorhome for years, it was big enough to cover almost anything and has 2 long bungees threaded through its outside edges. We used a couple of extra bungees around the middle to make it snug and to stop billowing. We used this for varying sized bikes and even a couple of wheelchairs on one occasion.
About 30 quid on amazon and you will never have to buy another
Take a look at Taylormade. I have had one for over 3 years and is used every month. They are not cheap but excellent quality. They also make one to suit electric bikes.
A day of all things motorhome and campervan. The show is held both in the main indoor arena and across the grounds. Catering, hot drinks and food options are available. Easy access to the site and free parking included. Win one of five pairs of day tickets