Putting down sound deadening sheets: where to do it?

After 200 miles in the Prius in one morning it was obvious that it was noisy from tire/road noise. We arrived exhausted by road noise.

What to do within a poor guy's budget? I thought about sheets of sound deadening material. And I thought (always a danger...) that the approach would be front doors on inside metal, front floors where the feet go and up a bit onto the firewall. For a product that's economic I found:

Noico 80 mil 36 sqft car Sound deadening mat, Butyl Automotive Sound Deadener, Audio Noise Insulation and dampening

It is $ 64 for 36 sq. ft. from Amazon. Roughly $2/sq.ft.

I haven't measured, but would 36 sq.ft. do what I have in mind?
Do I have the right places identified or are there others?

 

Based on comments so far: spare tire area and front doors are #1 areas to deaden. Agreed? Next areas? Suggestions?

I applied lithium grease to rubber gaskets on doors and windows some months back.

Found on the forum this interesting detailed installation of sound deadening material with photos:
Sound Deadening - Memorial Day Weekend(ish) Project! | PriusChat

 

Checking out Audio forum I found a thread that offers guidance
Sound deadening project complete...probably... | PriusChat

Here's a quote....
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Final results, purely subjective numbers from my point of view:

D'Amplifier mats in trunk and back seat area - probably around 10 - 15% total car noise reduction, but more importantly, 50% or more reduction in general noise from the rear area, that 'hollow' boomish/echoey kind of sound that comes from hatchbacks.

D'Amplifier mats in doors - another 10 - 15% noise reduction, not a lot, but now it's evident when driving in town and on highway. Combined with trunk/backseat area there now is a discernable difference.

Door matting on inside of door - 20%+ total noise reduction. Absolutely the biggest difference of all the work that was immediately noticed. Driving around on city streets was very, very quiet now, only the low rumbling was still evident, almost all higher pitched noise (whining,whoosing/rushing sound) is absent. On the freeway not quite as obvious, but still quieter, and now I don't touch the radio volume at all.

So each step helped a little, but when added together, the total reduction made a big difference.
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So, with a different brand of sound deadening material, it looks like front doors, rear trunk area.

 

Work done. Front doors: outer and inner metal panels. Rear trunk area. 9 sheets weighed about 3 lbs. each. I used 7+ sheets but will eventually put remaining sheet and 1/2 on metal under rear seat. Weight increase will be 27 lbs. Sound difference is significant for me. Standard (non JBL) audio head unit + I installed new/different (3 ohm and undersized) JBL speakers in all 4 doors. Road noise not done away with, but diminished. Satisfactory, not a miracle, nevertheless significant -- it is now a decent audio system. Thanks for various inputs to all....