I am indeed making a similar decision myself, single or double? I think I will be very pushed to get a double width in (5.2m RIB) so I would say it would be impossible on a 4m.
Speak to Leeway Composites (www.leewaycomposites.co.uk
) about consoles, he might be able to sort you out something. Otherwise look on ebay and boats and outboards. Alternatively, make your own! Do a search of the forum for "DIY console" or similar.
Hope that helps.