Welcome to the forum. Finding an awning to fit an Eriba is not an easy task and you really do need to go for a bespoke/model specific model. Your problem is compounded by the very low awning rail and whilst Reda in Holland do make some excellent awnings, availability will be an issue and costs will be high. They have been covered here in the past:- REDA awnings
If you want a good fit then you are very limited and I believe the Kampa Pop-Air 260 is probably your best option.
If you are prepared to sacrifice fit for something that may be more in keeping with the style/age of your Eriba then Just Kampers may be worth a visit. They did a retro style frame awning for VW campers that may be suitable.
Colin