Modeling long wires in circuits
There are three main issues that come to my mind:


Wire resistance: you already took it into account.
Wire inductance: you already took it into account, too (more on this later).
Transmission line effects: these will affect your circuit if the wires have a length which is comparable or greater than the minimum wavelength of the "signal".


About point 3: since you are not concerned with signal integrity (your "signal" is the power rail to the relay) you only need to worry if your switching times are too quick (some energy could be reflected back from the line toward your transistor ad fry it). If you switch the MOSET relatively slowly the frequency content of the "step" (a ramp, actually) won't hit that limit and you won't have problems, apart from higher power dissipation in the MOSFET during switching, but given the extremely low duty cycle of the system it is of little concern here probably. 

Anyway LTspice has two different models that can represent transmission lines: a lossy one and a non-lossy one. Excerpts from the online guide:


  T. Lossless Transmission Line
  Symbol Name: TLINE
  
  Syntax: Txxx L+ L- R+ R- Zo= Td=
  
  L+ and L- are the nodes at one port. R+ and R- are the nodes for the
  other port. Zo is the characteristic impedance. The length of the line
  is given by the propagation delay Td.
  
  This element models only one propagation mode. If all four nodes are
  distinct in the actual circuit, then two modes may be excited. To
  simulate such a situation, two transmission-line elements are
  required. See the schematic file
  .\examples\Educational\TransmissionLineInverter.asc to see an example
  simulating both modes of a length of coax.


and:


  O. Lossy Transmission Line
  
  Symbol Name: LTLIN
  
  Syntax: Oxxx L+ L- R+ R- 
  
  Example:
  
  O1 in 0 out 0 MyLossyTline .model MyLossyTline LTRA(len=1 R=10 L=1u
  C=10n)
  
  This is a single-conductor lossy transmission line. N1 and N2 are the
  nodes at port 1. N3 and N4 are the nodes at port 2. A model card is
  required to define the electrical characteristics of this circuit
  element.
  
  Model parameters for Lossy Transmission Lines
  
  [...table with all parameters omitted...]


Point 2 is more problematic, especially when switching the relay OFF: you could have an inductive kickback that destroys your MOSFET due to the wire inductance. Note that the diode across the relay won't protect you in this case. Thus a protection Zener at the switching transistor output (between drain and ground, cathode connected to drain) may be necessary to dampen that inductive kickback.

An article on the subject is here (not directly related to your specific case, though).