Solutions?

*Tune the woofer to lower frequency?
- u can immediately try this also, see which crossover frequency u like. if u have an EQ or bass boost u can try that too

*Face the woofer to rear window?Put the woofer to rear boot where?
- this one u can immediately try also

*Make bigger encloser?
- if none of the above works, then this is a cheaper alternative than the next one

*Or maybe not enough watt?
- changing to a better amp? yes, if u have the budget..

*Lower the watt tune from amp?
- how u intend to do this? not possible unless u change sub