Basically the SM +4 thing given in space ships 4 allows for making down to van size shuttles and such.

Below are guidelines for making normal large car size SM +3 vehicles and mini car size SM +2 things.

Hull Size Table
^SM ^Loaded Mass ^Length ^dST/HP^ Hnd/SR^
|+3 |3 tons |7 yards| 10 |+1/3|
|+2 |1 ton  |5 yards| 8  |+1/3|

^Armor^SM 3 USL^ SM 3 SL^SM 2 USL^ SM 2 SL^
|Light Alloy Armor|1|0.7|0.7|0.5|
|Metallic Laminate Armor|1.5|1|1|0.7|
|Advanced Metallic Laminate Armor|2|1|1|0.7|
|Nanocomposite Armor|3|2|2|1|
|Diamondoid Armor|5|3|3|2|
|Exotic Laminate Armor|7|5|5|3|

SM +3/+2 modules

Cargo: 0.15 tons(300 lb)/0.05 tons(100 lb)

Cloaking Device: $100k/$30

Contragravity Lifter: $30k/$10

Control room: 
    * SM 3:Need 4 spaces to fit in a SM 4 control room(smallest full control room) or 2 spaces to fit in a building/ground vehicle control(Pyramid 3-34 Alternate Gurps) room at half the regular SM 4 control room cost.
    * SM 2:Need 12 spaces to fit in a SM 4 control room(smallest full control room) or 7 spaces to fit in a building/ground vehicle control(Pyramid 3-34 Alternate Gurps) room at half the regular SM 4 control room cost.

Defensive ECM: $30k/$10

Enhanced, Science, Multipurpose, and Tactical Array: Array Level TL-6: $6k/$2 base cost

Force Screen: dDR 10/7 (at TL11) or dDR 15/10  (at TL12): sm 3: $50k/$150k sm 2: $15k/$50k

Fuel Tank: $1k 0.15 tons(300 lb)/$300 0.05 tons(100 lb)

Hangar Bay 0.1/0.03 tons(200lb/60lb) capacity $300/$100

Mining 0.015/0.005 tons(30/10 lb)/hour

Passenger Seating 
   * SM 3: one seat takes: 4 spaces for a full seat. 3 spaces for a nbc filterers only, 2 spaces for no life support. Cost: $1k*spaces.
   * SM 2: one seat takes: 12 spaces for a full seat. 9 spaces for a nbc filterers only, 6 spaces for no life support. Cost: $300*spaces.

Refinery 0.05/0.015 tons(20 lb/6lb)/hour

Other things are 10% the cost of SM 5 things for sm 3 and 10% of SM 4 things for SM 2. Same forbidden systems as SM 4.


Mag sails: http://www.sjgames.com/gurps/Roleplayer/Roleplayer29/MagSails.html