Annex inner tents

Mrs Dripdrap

Hi everyone, like all happy campers we cannot wait for the nights to get lighter and the season to get into full swing. In readiness for the new season we have purchased an annex to fit our awning (Vango Sonoma Air) however this did not come with the inner tent so my question is- does any sloping inner tent fit these type of annexes or are they specific to own brands?