Thanks for the input guys
As much as possible i'd like to keep my budget to a low. Getting a normal sub with custom fiber box would cost be much more right? Moreever i'll need to dampen the area behind which might add onto the cost.

Im looking towards RM600 give or take for a proper underseat sub. This includes driver, 2nd hand amp and DIY MDF enclosure. You think can make it ah .

The pioneer low mount would be about RM240 or so. So that leaves RM360 for the rest =.=.

I am actually considering whether to get a low mount sub with seperate amp, vs active sub.

Low mount sub choices like the above.
But currently from my measurement, my car underseat only have about 4.2" of height.
If subtract thickness of MDF board, seems like the mounting depth of the sub has to be very low in order to fit in there .

So far got 2 choices only Pioneer TS-SW841D & Earthquate SWS-8X. I was wondering whether these 2, matched with a decent cheap amp, will it be better than just getting an active sub like the Steelmate active sub?

Thanks!