Creating solid from a 3d car model

I have created a 3d model of my own car using simple surfacing tools. But i cant seem to create a solid from within in order for me to run CFD analysis in Fluent. Appreciate any help from all.

I will provide my cad file below.

Dropbox - fullassy.x_t

Please let me know what can i do... Kinda lost right now.

Thanks,

Jun

SolidworksSurfacing